Froth flotation is a well-known process for separating valuable minerals from the remaining gangue in a mineral ore body. To obtain the valuable mineral, the ore is firstly ground, for example, in an AG, SAG or rod mill which is often followed by further grinding in a ball mill. The resultant slurry is then passed through a particle sizing apparatus such as a cyclone to limit the size of the particles to a predetermined value eg 0.1-05 mm.
Traditionally, collectors, frothers, activators and various other additives are added to the slurry prior to its entry into the rougher/scavenger circuit where the desired valuable mineral is floated off from the remaining tail. The resultant concentrate is then fed to a cleaner/re-cleaner flotation circuit to undergo further processing. Optionally, more collector/frother malt be added at this time and the slurry may be reground prior to entry into the cleaner/re-cleaner circuit.
It is vital to successful flotation to maintain the hydrophobic nature of at least the surface of the valuable sulphide mineral. This is ordinarily accomplished by adding an anionic collector to the slurry. It is important, however, to add the correct collector and in the correct amount.
There has to date been several previous studies in regard to collectorless flotation of minerals, for example, chalcopyrite. If chalcopyrite ore is broken in a clean environment and subjected to flotation with air in an aqueous environment, it has been shown to form a metal deficient sulphide. If the material is oxidised further it is believed that it forms iron hydroxide and elemental sulphur. The form of the equation for some metal sulphide minerals in alkaline environments is as follows:MS+xH2O=M1-xS+xMO+2xH++2e 
If the metal sulphide is oxidised further then the sulfur ends up being elemental sulfur as shown in the following equation:MS+2H2O=M(OH)2+S0+2H++2e−
The metal deficient sulphide M1-xS and the sulfur element S0 are the hydrophobic species. Flotation can happen as long as the metal oxides/hydroxides formed by the reaction are solubilised. Excessive oxidation can produce thiosalts and ultimately sulphate. These ions together with the metal ions may react and re-adsorb as hydrolysis products on to the mineral producing hydrophilic surfaces.
With chalcopyrite the equation forming the sulfur element is:CuFeS2+3H2O=CuS+Fe(OH)3+S0+3H++3e 
The collectorless flotation of chalcopyrite requires that the flotation occurs in a neutral or slightly oxidising environment. Previous studies have shown that freshly fractured flotation of chalcopyrite increased when the redox potential (Eh) was in the neutral or slightly oxidising region. The flotation process also requires that the surface of the minerals being floated be as clean as possible. Previous studies have compared the effects on flotation recovery of a freshly fractured sulphide mineral versus an ore air oxidised for three weeks. The result was that the air oxidised minerals did not achieve the same recovery as the freshly fractured minerals.
Accordingly, it would appear that collectorless flotation of sulphide minerals is less likely to proceed unless the mineral surfaces are clean and the flotation is conducted in an oxidising environment. There are a number of situations which may cause the surfaces of mineral not to remain clean including:                iron ions (from metal balls or mill liners) in solution after the ore has been through the ball mill. These ions may then form hydroxide which may deposit on the surface of the minerals,        recycled water containing ions that eventually react with metal ions in the system and then re-adsorb on the surfaces of the minerals.        
There are a number of techniques which have been previously attempted to reduce the amount of these materials remaining on the surfaces of the particles including high intensity conditioning vessels and cleaning agents like sodium sulphide. Collectors like xanthate have also been suggested to perform the function of cleaning the surface of the minerals of these hydroxides in the first instance. Once the surfaces have been cleaned, the sulphide mineral can float due to the collector which attaches to the mineral making it hydrophobic.
As mentioned above, although there is some dispute, it is generally thought that collectorless flotation of certain sulphide minerals require an oxidising environment.
All flotation machines can be arranged to provide an oxidising environment required by the reaction to render the sulphide mineral particles hydrophobic. However, as indicated above, if oxidation proceeds too far, thiosalt and eventually sulphate may form from the sulfur oxidation which may react with a metal ion in the solution forming metal sulphide.
This is a perennial problem with conventional production mechanical flotation cells when attempting collectorless flotation. The residence time for a typical mechanical cell is about three to five minutes. This long residence time and the increased Eh in a mechanical cell causes excessive oxidation of the slurry thereby producing hydrolysis products which deposit on the surface of the minerals and may render them hydrophilic in nature ie difficult to float.
The present invention seeks to overcome at least some of the disadvantages of the prior art or provide a commercial alternative thereto.